Method of making diamond-faced articles



KIYOSHI INOUE 3,305,331

METHOD OF MAKING DIAMOND-FAGED ARTICLE Original Filed Feb. 28, 1961 4Sheets-Sheet 1 Feb. 21, 1967 INVENTORI K/YOSH/ INOUE 9Q CROSS AGENT.

Feb. 21, 1967 KIYOSHI INOUE METHOD OF MAKING DIAMOND-FACED ARTICLEOriginal Filed Feb. 28, 1961 4 Sheets-Sheet 2 INVENTOR.

K/YQS'H/ W005 AGENT.

Feb, 2E, W67 KIYOSHI INOUE ,35,331

METHOD OF MAKING DIAMOND-FACED ARTICLE Original Filed Feb. 28, 1961 4Sheets-Sheet 5 INVENTOR. K/YOSH/ IIVOUE AGENT.

F 21, 1967 KIYOSHI INOUE 0 31 METHOD OF MAKING DIAMOND-:FACED ARTICLEOriginal Filed. Feb. 28. 1961 4 Sheets-Sheet 4 INVENTOR.

AGENT.

United States Patent Ofiice 3,3053% Patented Feb. 21, 1967 3,305,331METHOD OF MAKING DIAMOND-FACED ARTICLES Kiyoshi Inoue, 182 3-chome,Tamagawayoga-machi, Tokyo-to, Japan Original application Feb. 28, 1961,Ser. No. 92,284, now Patent No. 3,207,582, dated Sept. 21, 1965. Dividedand this application June 16, 1965, Ser. No. 490,756 Claims priority,application Japan, Mar. 3, 1960, 35/ 6,569 7 Claims. (Cl. 51-307) Thisapplication is a division of application Ser. No. 92,284, filed February28, 1961, now US. Pat. No. 3,207,582 of September 21, 1965.

The present invention relates to a method of synthesizing diamondparticles from amorphous carbon or graphite, and more particularly to amethod of directly synthesizing diamond particles from amorphous carbonor graphite by utilizing the high temperatures and impulsive highpressures produced by an electric discharge.

Although it is well known that diamond, graphite and amorphous carbonall consist of the same element, i.e., carbon, they are consider-ablydifferent in appearance, as well as with respect to their physical andchemical properties due to their different crystalline structure.Diamonds are widely used as cutting tool tips for machine tools, wiredrawing dies or ornaments, because they have the highest hardness valueof all substances and because it is possible to impart to them a specialluster by grinding and polishing. Natural production of diamond islimited, and methods of artificially producing diamonds, in a convenientand effective manner, had not hitherto been developed. On the otherhand, amorphous carbon and graphite constituted also of elemental carbonas pointed out above are produced naturally in large quantities and itwould be quite natural to consider that diamonds could be artificiallysynthesized by subjecting amorphous carbon or graphite to definitephysical and chemical conditions to alter their crystalline structures.

While there has not yet been any definite determination as to What thephysical and chemical conditions necessary in order to alter thecrystalline structure of carbonaceous material for obtaining theso-called diamond crystalline lattice, it has been presumed that a hightemperature of over about 4000 C. and a high pressure of over about 200tons per square centimeter would be necessary. As a result of extensiveexperiments, I have found that above mentioned conditions of hightemperature and high pressure can be produced under certain conditionsby spark discharges between electrodes and I have succeeded insynthesizing diamond particles from graphite or amor' phous carbon.

More particularly, I have produced minute particles of diamond accordingto a method which comprises disposing a pair of electrodes made ofgraphite to define a minute gap therebetween in a liquid havingpredominant properties of dielectrics (if required, it may be anelectric conductive liquid or electrolyte), and producing an electricdischarge across the graphite electrodes to yield the particles. Uponexamining the minute particles having a specific gravity of about 3.5with X-ray analyzing devices, I have ascertained a line of 3.56 A.representative of the lattice constant of the diamond. Scratch testswere also made wherein these minute particles were tested on a mirrorfinished tungsten carbide plate and I have found that the abrasiveproperty of the particles seems to be higher than that of the naturaldiamond. Thus I believe that I have succeeded in the synthesis ofdiamond particles having hardness sufiiciently larger than suchextremely hard materials as tungsten carbide.

My experiments also revealed that colored diamonds could be obtained bydisposing a pigmenting substance near the graphite electrodes at thetime of producing the electric discharge therebetween.

According to my method of synthesis, electric discharge is produced in aliquid to subject graphite used as the electrodes to an extremely hightemperature and high pressure (impulsive pressure caused by electricdischarge) condition, whereby it is possible to directly and easilysynthesize diamond particles from graphite. Thus, it is possible toproduce grinding discs which, heretofore, have been termed diamondwheels, by producing electric discharges on the surface of a graphitedisc or of a disc which is prepared by sintering a mixture of particlesof iron, nickel, chromium and graphite and maintained in a workingliquid, whereby to transform the graphite particles contained in thedisc surface into diamond particles. It is also possible to producediamond needles by applying a layer of minute particles of carbon orgraphite on the surface of a needle for use with phonograph records andthereafter producing a spark electric discharge on said surface of saidneedle maintained in the liquid. The diamond wheels and diamond needles(styli) are only examples of the products produced by my method ofsynthesizing diamond particles, and I believe that this invention can beequally applied to many other applications.

An object of this invention is to provide a novel method of producingtools and other articles having surfaces of very high abrasive propertyby forming thereon (in situ) diamond particles which are synthesizedfrom graphite or amorphous carbon by utilizing an electric discharge.

Further objects of this invention will become apparent from thefollowing detailed description of my improved method of synthesis withreference to the accompanying drawings, in which the same or equivalentmembers are designated by the same reference numerals and in which:

FIG. 1 is a diagrammatic representation of essential portions of anapparatus for carrying out my improved method of synthesizing diamondparticles from graphite;

FIGS. 2a, 2b and 2c are diagrammatic elevational views showing theconstruction of improved electrodes for increasing the eifectiveimpulsive pressure of an electric spark discharge;

FIGS. 3a to 3g inclusive illustrate another improved construction of theelectrodes for preventing damage thereof or for coloring the diamondparticles synthesized;

FIG. 4 shows a modified apparatus adapted to concentrate the hightemperature and high pressure produced by the electric discharge, thusincreasing their function;

FIG. 5 shows an improved apparatus for increasing the high temperatureand high pressure still further at the discharge site;

FIGS. 6a, 6b and 6c are diagrams for explaining an improved method ofseparating diamond particles contained in the working liquid;

FIG. 7 is a diagram for explaining a single step separating method;

FIGS. 8a and 8b are diagrammatic views for explaining the method ofproducing a diamond wheel according to my invention; and

FIG. 9 is a diagrammatic view for explaining a method of producing adiamond needle in accordance with my invention.

Referring now to FIG. 1 of the accompanying drawing, reference numerals1 and 1 represent electrodes made of amorphous carbon or graphite anddisposed to oppose each other with a small discharge gap therebetween.An electric discharge tank 2 is filled with a di electric liquid. At theupper and lower portions of the discharge tank 2, there are perforations3 and 3' adapted to receive electrodes .-1 and 1', respectively, thespace between the electrodes and the perforations 3 and 3' beinghermetically sealed by spacers 4 and 4'. The electrode 1 is held at theoutside of the discharge tank 2 by means of an electrode chuck 5 havinga rack and pinion device 6 at its upper portion. The rack and piniondevice 6 is driven by a motor 7 for advancing the electrode 1 into thedischarge tank 2. Thus, the length of the discharge gap is adjustable toestablish the discharge-initiating voltage, to start discharge and tocompensate electrode consumption. Similarly, the electrode 1 is held bychuck 5' at the outside of the discharge tank 2, and lead wires 8 and 9are respectively connected to electrodes l and 1'. The lead wires areconnected across the terminals of a discharge condenser 10, which, inturn, is connected with a direct-current charging source 12 through astabilizing impedance 11.

With this device, if the voltage across the discharge gap between theelectrodes 1 and 1' reaches the critic-a1 discharge value, the electriccharge stored in the condenser 10 will be discharged through the gapbetween the electrodes 1 and .1. Since the terminal voltage of saiddischarge condenser 10 is decreased due to said discharge, said terminalvoltage is prevented from rebuilding rapidly by the action of thestabilizing impedance 11 so that the discharge across said electrodeswould stop immediately and there is no tendency to form a continuousare, but intermittent spark discharge is permitted' Thus, when thedischarge is terminated, the terminal voltage of the discharge condenser10 will begin to increase again until the discharge gap will again breakdown. In this way, the electrodes 1 and 1 will repeatedly discharge andthe impulsive pressure and high pressure created by the spark dischargewill cause the amorphous carbon or graphite constituting the electrodesto melt and disperse it, as small particles, into the surroundingliquid.

Carbon particles thus dispersed in the liquid will be fused by hightemperature of the electric discharge and then converted into diamondsunder the influence of impulsive force of the discharge while they arecooled in the liquid. Thus, it is evident that all physical and chemicalconditions necessary for the synthesis of.diamonds are fulfilled in thespark discharge between the electrodes immersed in a liquid.

Since due to the repeated spark discharge both the electrodes 1 and 1will be gradually consumed to increase the discharge gap therebetween,the driving motor 7 is arranged so as to be controlled in accordancewith a quantity related to the discharge current to lower the electrode1 towards the electrode 1' through the rack and pinion device 6, tomaintain a constant gap width.

According to my experiments, when a discharge energy of 5000 joules wasdischarged between the electrodes to disperse minute particles ofelectrode material, I have ascertained production of minute diamondparticles in said dispersed particles was confirmed from the result ofX-ray diffraction test and scratch test made on a mirrorfinishedtungsten carbide plate.

In this regard, I have found that yield of diamond particles could beincreased by causing a high energy discharge between electrodes afterthe pressure in the discharge tank 2 has been increased by vaporizationof the liquid and expansion thereof with temperature increase caused byinitial several discharges. vice shown in FIG. 1, it is necessary totake care that the discharge formed across the electrodes 1 and 1' doesnot degenerate to an arc discharge. Thus, although are discharge causesthe electrodes 1 and 1' to be heated to a very high temperature due tothe heat generated thereby, since the discharge is continuous, it isimpossible to obtain the necessary impulsive pressure. On the contrary,by using a spark discharge the requisite impulsive pressure can beobtained.

According to the result of my experiment which was Also, with the demadeby using the device shown in FIG. 1, it was found that better resultswere obtained when the voltage of the discharging direct current source12 was low and the capacitance of the discharge capacitor 10 larger thanin the case wherein the voltage of the source is high and thecapacitance of the condenser is small, assuming that the energy ofdischarge is the same for both cases, although the reason for this isnot well understood.

In order to increase the impulsive pressure which is generated by thespark discharge and acts upon the discharging points, it is advantageousto use a liquid which volatilizes easily, has a large volumetricexpansion coefficient and is non-compressible. It is believed thatexplosive mechanical force which is created simultaneously with thespark discharge is also effective. According to my experiments,kerosene, carbon tetrachloride and the like are preferable liquids togive good results.

It was also confirmed that the diameter of the diamond particles couldbe increased when solutions of hydrocarbons are used and I think thatthis is due to the fact that such solutions as described above have afunction of promoting the growth of the diamond particles when they aresynthesized. Although it is not yet clearly understood why hydrocarbonsolutions promote the growth of diamond particles, I presume that thecarbon elemental freed by the decomposition of the hydrocarbon at thehigh temperature of the spark discharge participates with the meltedcarbon of the electrode. According to my experiments, diamond particleshaving maximum diameter of about 14M) were produced when kerosene oil (ahydrocarbon compound) and a discharge energy of 5000 joules were used,whereas particles of maximum diameter of 16ml) were obtained with thesame discharge energy when a solution of hydrocarbon corresponding to CH 0 +H O was used.

FIGS. 2a, 2b, and 20 show various constructions of electrodes forincreasing the impulsive pressure produced by the spark discharge. InFIG. 2a, slots 13 and 13"are provided near the center of the electrodes1 and 1', in FIG. 2b the opposing surfaces of the electrodes areprovided with concave portions 14 and 14', respectively, together withseveral longitudinal slots 13 and 13'; in FIG. 20, concave portions 14and 14 are provided at the central portion of the electrodes 1 and 1.

By providing the slots 13 and 13 and/or the concave portions 14 and 14'for the electrodes 1 and 1, as shown in the drawing, the impulsivepressure created by the spark discharge will act convergently upon theslots or concave portions to impart a large impulsive pressure to themelted portion of the electrodes.

It was found that the construction of the electrodes as shown in FIG. 2bis better than that shown in FIG. 20. It is believed that this is mainlydue to concentration of the discharge energy at a minute area of theprojecting portions of the electrodes of FIG. 2b, because dischargepoints have a tendency to be formed thereon.

When diamond particles are synthesized by forming spark discharge in thedevice shown in FIG. 1, portions of the electrodes 1 and 1' which arenot yet melted by the electric discharge have a tendency to bedisintegrated by the impulsive pressure due to discharge. It isnecessary to reinforce the electrodes 1 and 11' so as to concentrate theimpulsive pressure to the discharge points alone and to make it possibleto cause repeated discharge at these points.

FIGS. 3e and 3g show constructions of electrodes 1 and 1' havingreinforcing means, which, in the case of FIG. 3e, comprises metallicrings 15 and 15 surrounding the electrodes 1 and 1', respectively.

FIG. 3g shows another construction of the reinforced electrodes 1 and 1,each comprising alternately sections 17 of amorphous carbon or graphiteand reinforcing sections 16 of a metal which are clamped together byreinforcing metal cylinders 15 and 15, tightly fitting around them.Thus, only the discharge points which are heated to molten states by theheat of the spark discharge are gradually separated and high temperaturemolten carbon particles of high temperature will be transformed intodiamond particles under the action of the impulsive high pressureimparted thereto.

By experiments I have found that, if amorphous carbon or graphite wereplaced near the spark discharge points together with titanium oxide,simultaneously with the transformation of carbon particles into diamondparticles caused by the high temperature and high pressure of the sparkdischarge, titanium oxide is included in the diamond particles, thusproviding pink or colored diamond particles.

FIG. 3a shows a construction of the electrodes wherein the body of theelectrodes 1 and 1' is made of titanium oxide and particles 18 and 18 ofamorphous carbon or graphite are attached to the tip of the electrodes,or conversely the body of the electrode 1 and 1 is made of amorphouscarbon or graphite and titanium oxide particles 18 and 13' are attachedto the tip of the electrodes.

Similarly, FIG. 3b shows an electrode construction wherein theelectrodes 1 and 1' are composed of titanium oxide or graphite andintermediate electrodes 18 made of graphite or titanium oxide are used.In this figure, the intermediate electrodes 18 are disposed adjacent thedischarge gap between the main electrodes 1 and 1' and supported byflexible means, with respect to the main electrodes 1 and 1; but it isnot always necessary to electrically connect said intermediate electrodeto the main electrodes.

In FIG. 3c, one electrode 1 is composed of amorphous carbon or graphitewhile the other electrode 1 is composed of titanium oxide. FIG. 3a showsan electrode construction wherein both the electrodes 1 and 1 arecomposed of amorphous carbon or graphite 17 and of titanium oxide 16which are disposed as shown in FIG. 3d.

FIG. 3c shows an electrode construction wherein reinforcing metal rings15 and 15' are fit around the electrodes 1 and 1' made of graphite, asalready explained hereinbefore, but when it is desired to synthesizecolored diamond particles, titanium oxide is used as said reinforcingmetal ring 15 and 15. This construction not only provides a coloringeffect upon diamond particles, but also reinforces them.

FIG. 3 shows another electrode construction on formed by sinteringtogether particles 16 of amorphous carbon or graphite and titanium oxideparticles 17.

FIGS. 3g and 3g show still another electrode construction whereinreinforcing metal sections 16 and amorphous carbon or graphite sectionsare alternately disposed; these sections are surrounded with reinforcingmetal rings 15 and 15' made of titanium oxide, said metal rings causingreinforcing function of the electrodes as well as the diamond coloringfunction just like the construction shown in FIG. 3e. While theseelectrodes are not provided with the reinforcing metal rings, ifnecessary they can be provided with such reinforcing metal rings 15 and15 as shown in FIGS. 3e and 3g, 3g.

Also use of titanium oxide as the electrode reinforcing metal section 16or reinforcing metal ring 15 is advantageous in that it can afford boththe reinforcing effect for the electrodes 1 and 1 against the impulsivepressure and coloring function of the diamond particles, as abovedescribed.

Electrode constructions shown in FIGS. 3a to 3g inclusive are alsoeffective for utilizing a catalyst to promote synthesis of diamondsparticles.

By experiment, I have found that, when diamond particles are synthesizedfrom graphite by means of spark dicharge, if at least one kind of metal,such as chromium, manganese, cobalt, nickel, platinum and the like, andtheir oxides or chlorides are positioned near the discharge point, suchmetal, oxide or chloride thereof will act as a catalyst to promote thesynthesis of diamond particles. For example, in the absence of asubstance affording a catalytic function, spark conditions correspondingto a temperature of 3600 C. and a pressure of 200 tons per squarecentimeter would be necessary, thus requiring a large discharge energy,but when the catalyst is incorporated, synthesis was successfullycarried out with spark conditions corresponding to a temperature between1500 and 2000 C. and under a pressure of about tons per squarecentimeter and with an apparatus simplified accordingly.

The means to dispose the catalyst metal adjacent the discharge point maytake various forms. Thus, a construction shown in FIG. 3a wherein thecatalyst metals 18 and 18' are attached to the amorphous carbon orgraphite electrodes 1 and 1'; that shown in FIG. 3b wherein the catalystmetal is interposed as the intermediate electrodes 18; that shown inFIG. 3c wherein one of the electrodes 1 is made of the catalyst metal;that shown in FIG. 3d wherein the electrodes 1 and 1' are composed oflaminated sections of amorphous carbon or graphite 17 and catalyst metal16; that shown in FIG. 32 wherein the reinforcing metal rings 15 and 15'are made of the catalyst metal, that shown in FIG. 3 f wherein theelectrodes 1 and 1' are prepared by sintering a mixture of particles ofcarbon and particles of the catalyst metal; and that shown in FIG. 3gwherein the electrodes 1 and 1' comprise a plurality of laminated layersof amorphous carbon 17 and catalyst metal 16 which are clamped byreinforcing metal rings 15 and 15 or wherein the rings are made of thecatalyst metal are also effective means.

FIG. 4 illustrates a modification of the apparatus for embodying thepresent invention. While in FIG. 1, heat and impulsive pressure due toinstantaneous formation of a spark discharge are produced by a singledischarge across electrodes, in FIG. 4, the electrodes are first broughtto a molten state by a high temperature created by an arc discharge, andthereafter an impulsive pressure created by a spark discharge is appliedto said molten portions of the electrodes whereby to eifecttransformation of the amorphous carbon or graphite constituting theelectrodes into diamond particles.

Referring to FIG. 4, rod-shaped electrodes 1 and 1' are made ofamorphous carbon or graphite and are connected with an arc source 20 viaan impedance 19 for stabilizing arc discharge to maintain an arcdischarge between said electrodes 1 and 1' to heat the tip thereof at anelevated temperature. Hollow cylindrical electrodes 21 and 21 arerespectively arranged to surround electrodes 1 and 1 with a small gaptherebetween. This small gap between said cylindrical electrodes 21 and21' and the gap between said electrodes 1 and 1 are disposed in the samehorizontal plane, but it is preferable to arrange said electrodes insuch a manner that the electrodes 1 and 1' are positioned somewhat lowerthan the gap between the cylindrical electrodes 21 and 21' so as tocause intersection of the tip 22 of one of the electrodes 1 and 1' withthe horizontal plane defined by the small gap between said cylindricalelectrodes 21 and 21' in order to cause the impulsive pressure createdby a spark discharge between the cylindrical electrodes 21 and 21 to actmainly in the direction perpendicular to the axes of the electrodes 21and 21'. The cylindrical electrodes 21 and 21 are connected across theterminals of a discharge condenser 26 through lead wires 23 and 24 and aswitch 25; the terminals of said condenser are connected with a sourceof direct current 27 through an impedance 28 for stabilizing thecharging current.

The electrode assembly shown in FIG. 4 is in a sealed discharge tank 2,as shown in FIG. 1, filled with a liquid. At first an arc discharge isformed between the electrodes 1 and 1' by the electric source 20 to heatthe tips of the electrodes 1 and 1' to incandescent state. The switch 25is then closed to discharge the condenser 26 through the gap betweencylindrical electrodes 21 and 21 whereby to establish a spark dischargeacross said cylindrical electrodes 21 and 21' at a repetition frequencydetermined by a time constant of said impedance 28 for stabilizing thecharging current and condenser 26. Due to this repeating spark dischargebetween said hollow cylindrical electrodes 21 and 21, an impulsivepressure will be applied to the electrodes 1 and 1', thus supplying thispressure as a pinch force acting in all radial directions from the gapbetween the cylindrical electrodes, to the tips of the electrodes 1 and1' which have been previously brought to molten state by said aredischarge, whereby it is possible to obtain the high temperature andhigh pressure conditions necessary for the synthesis of diamondparticles.

While, in FIG. 4, the distance between the electrodes 1, 1 and thehollow cylindrical electrodes 21, 21' is shown as relatively large,actually these two pairs of electrodes are closed enough to causetransmission of the impulsive pressure created by the spark dischargebetween the hollow cylindrical electrodes 21 and 21 to the incandescenttips of the electrodes without any attenuation.

Although it is desirable to cause the impulsive pressure to act upon theincandescent tips of the electrodes 1 and 1 equally in all radialdirections, when each of the cylindrical electrodes 21 and 21' is madeas an integral unit as shown in FIG. 4, the spark discharge between themmay drift laterally from time to time resulting in unequal radialpressure upon the electrodes 1 and 1, which is not effective to create apinch force. In order to prevent spark discharge points from beingformed on only one side of the hollow cylindrical electrodes 21 and 21',it is preferable to divide these cylindrical electrodes into a pluralityof axially divided sections and to connect each of these sectionsindividually to the source of impulse current. By so dividing saidhollow cylindrical electrodes and by producing simultaneouslyindependent spark discharges on said separated electrode sections, it isable to apply a uniform impulsive pressure to the incandescent portionsof the electrodes 1 and 1' from all radial directions, thus enabling toincrease the size of diamond particles being synthesized. Thus, in FIG.4, if the incandescent tips 22 of the electrodes 1 andl' are subjectedto a uniform impulsive pressure in all radial directions from saidsurrounding hollow cylindrical electrodes, the molten carbon particleswhich have been formed by previous arc discharge would be dispersed inthe state of larger particle size than in the case of using theapparatus shown in FIG. 1. Furthermore, it is possible to subject thesedispersed molten carbon particles to a uniform impulsive high pressuresupplied in all radial directions, thus enabling transformation of allthe dispersed carbon particles into diamond particles.

FIG. illustrates an apparatus wherein an explosive is exploded to obtaina necessary impulsive pressure to synthesize diamond particles. In thisfigure, similar to the apparatus disclosed in FIG. 1,a pair ofelectrodes 1 and 1' made of amorphous carbon or graphite is disposed ina working liquid to define a small discharge gap between them. Theseelectrodes extend through the openings 3 and 3' provided in the sidewall of the discharge tank 2 and spacers 4 and 4' are provided tohermetically seal the gap between electrodes 1 and 1 and the dischargetank 2. At the positions inside the upper and lower wall of thedischarge tank 2, there are secured platforms 30 and 30 for mountingblasting caps, and on said platforms are secured blasting caps 31 and 31serving as the explosive in positions perpendicular with respect to thedischarge gap defined by said discharge electrodes 1 and 1', saidblasting caps 31 and 31 being connected to terminals 33 of an ignitionsource not shown through ignition conductors 32, 32. The electrodes 1and 1' are connected to terminals 34 of a source (not shown) of impulsewave for producing an electric discharge.

When this apparatus is to be used for synthesizing diamond particlesunder an impulsive pressure, a spark discharge is produced across theelectrodes 1 and 1' to melt a portion of amorphous carbon or graphiteconstituting said electrodes 1 and 1 while at the same time the blastingcaps 31 and 31' are ignited to explode to impress the impulsive pressureproduced thereby to said spark discharge point.

In addition, with such an apparatus, it is easy to produce an impulsivepressure of the pressure on the order of to tons per square centimeter,so that it is not always necessary to produce a spark discharge acrosssaid electrodes 1 and 1', but it may be possible to produce an arcdischarge between them for obtaining the required high temperature whileutilizing the high impulsive pressure produced by said explosion.

FIGS. 61:, 6b and 60 show diagrams for explaining a simple method ofseparating the produced diamond particles from the liquid. While thereare many well known methods of separating the diamond particles from theworking liquid containing them, all of such methods accompany extremedifliculties, because all of the minute particles contained in theworking liquid have not been transformed into diamond particles, but themixture contains some proportions of unconverted carbon particlestogether with other particles, and mere separation of minute particlesfrom liquid is not necessarily equivalent to recovery of diamondparticles. Accordingly, in the method described in FIG. 6, specificgravity is utilized wherein the minute particles are separated from theworking liquid by filtration or evaporation and thereafter the separatedminute particles are put in a liquid having a specific gravity of 4contained in a vessel 34, as shown in FIG. 6a. Then, by the differencein specific gravities, particles 35 having a specific gravity higherthan 4 will precipitate the bottom of the vessel 34 whereas particles 36having a specific gravity lower than 4 and containing diamonds willfloat on the surface of the liquid. These particles floated on thesurface of the liquid are then removed to vessel 34' containing a liquidhaving a specific gravity of 3.8, as shown in FIG. 6b. According to thesame principle as described above, minute particles 37 having a specificgravity of from 3.8 to 4 will precipitate to the bottom of the vessel34', Whereas particles 38 having a specific gravity lower than 3.8 andcontaining diamonds will float 0n the surface of the liquid. Thereafter,when the particles floated on the surface of the liquid are thrown intoa liquid having a specific gravity of 3.3 and contained in a vessel 34",as shown in FIG. 60, the mass of particles will be separated intofloating and precipitated portions. Then the particles 40 'having aspecific gravity lower than 3.3 and floated on the surface of the liquidare removed and minute particles 39 precipitated on the surface of. thevessel 34" are collected to separate therefrom diamond particles havinga specific gravity of 3.5.

/ Separation of diamond particles of the specific gravity of 3.5 fromminute particles having .a specific gravity of 3.5 to 3.8 is easier thanthe separation of diamond particles from the liquid, because it can beconsidered that nearly all of the particles having a specific gravity of3.3 to 3.8 are diamond particles.

FIG.-7 illustrates a method of separating diamond particles by aseparating method according to specific gravity in the same manner as inFIG. 6. In FIG. 7, liquids having specific gravity of 4, 3.8, and 3.3,respectively, are poured into a vessel 34. Then, due to differences inspecific gravities, particles 35 having a specific gravity higher than 4will precipitate on the bottom of the vessel 34, particles 36 and 37having a specific gravity between 3.8 and 4 will float at the interfacebetween the liquids having specific gravities of 3.8 and 4,respectively, particles 38 and 39 having a specific gravity between 3.3and 3.8 will float at the interface between the liquids having specificvgravities of 3.3 and 3.8, respectively, and particles 40 having aspecific gravity higher than 3.3 will float on the surface of the liquidhaving a specific gravity higher than 3.3. Diamond particles will haveto exist at the interface between liquids having specific gravities of3.3 and 3.8, respectively, so that it can be considered that nearly allof said particles are diamond particles and can be separated as diamondparticles.

The methods of separation by specific gravity as shown in FIGS. 6 and 7are very effective for separating the diamond particles producedaccording to this invention.

More particularly, the method illustrated in FIG. 7 was found to be mosteffective, because there is suflicient time for the minute particles toprecipitate.

FIGS. 80! and 8b show diagrams for explaining a method of manufacturinga diamond wheel, that is, a well known grinder disc in accordance withthe present invention.

Referring to FIG. 8a and 8b, at first a disc element 41 is made ofgraphite, or made by sintering particles of iron or nickel and particlesof graphite or by adhering graphite particles to the surface of a discmade of nickel, iron, chromium and the like. The disc element 41 thusprepared is then disposed in a working liquid contained in a dischargetank, not shown, to oppose to another electrode 42, as shown in FIG. 8a,and a spark dis-charge is repeatedly produced on the entire surface ofthe .disc element 41 While moving theelectrode 42 or disc element 41,whereby the graphite particles 43 on the surface of the disc element 41are converted to diamond particles 43, as shown in FIG. 8b, thusobtaining a diamond wheel. The diamond wheel produced, or the grindingdisc with diamond particles on its surface can be used as a working toolor the like.

FIG. 9 is a diagram for explaining a method of producing a diamondneedle for use in playing phonograph records in accordance with themethod of the present invention. At first, graphite particles areadhered onto the surface of a phonograph needle 44, or the pointed tipof the needle is formed of graphite particles or of a mixture comprisinggraphite particles and particles of other metal. The phonograph needle44 thus formed is then utilized as one electrode, and the otherelectrode 42 is disposed to oppose the pointed portion of said needle.By producing an electric discharge in a liquid contained in a dischargetank, not shown, or by utilizing electric are together with anotherimpulsive pressure producing means, as in the case of FIGS. 4 and 5, thepointed end of the phonograph needle 44 is transformed into diamondparticles 43, thus providing a diamond needle, which is useful as a longlived needle for playing phonograph records.

Articles shown in FIGS. 8 and 9 represent a few illustrative examples ofarticles which can be produced according to my method of synthesizingdiamond particles and it will be obvious to those skilled in the artthat many pther articles can be produced according to my method ofsynthesis, and that this invention can be applied for th production ofarticles required to have 'high hardness.

What I claim is:

1. A method of making a diamond-faced article, com prising the steps of(a) providing an electrically conductive metallic sup port with a carbonportion bonded to said suppor and exposed at a surface region thereof;

(b) spacedly juxtaposing an electrode with at least par of said carbonportion to form a spark gap there with;

(-c) surrounding the juxtaposed parts of said electrode and said carbonportion with an ambient liquid fill ing said gap; and

(d) effecting at least one impulsive spark discharge across said gapbetween said carbon portion and said electrode with sufiicient dischargeenergy to generate a temperature and pressure converting at least partof said carbon portion to diamond.

2. The method defined in claim 1 wherein said support is a wheel havingsaid carbon portion extending over an annular zone thereof, said methodfurther comprising the steps of successively juxtaposing said electrodespacedly with a multiplicity of regions of said zone in said liquid, andrepeatedly applying a discharge electrical potential across said supportand said electrode to effect intermittent and repeated spark dischargesat said multiplicity of regions to form diamond throughout said zone.

3. The method defined in claim 2 wherein said support is tflprmed bybonding graphite and metallic particles toge er.

4. The method defined in claim 2 wherein said support is a metal diskhaving a graphite layer bonded to a surface thereof.

5. The method defined in claim 1 wherein said liquid is a dielectric andsaid discharge energy is about 5000 joules.

6. The method defined in claim 1 wherein said support is elongated andis formed with a graphite tip at an end thereof.

7. The method defined in claim 6 wherein said graphite tip is formed bysintering graphite and metal particles together.

References Cited by the Examiner UNITED STATES PATENTS 2,068,848 1/1937De Bats 51307 2,960,759 11/1960 Bondley 29-l 69.5 3,101,260 8/1963Cheney 23209.1 3,141,746 7/1964 De Lai 51-307 ALEXANDER H. BRODMERKEL,Primary Examiner. D. J. ARNOLD, Assistant Examiner,

1. A METHOD OF MAKING A DIAMOND-FACED ARTICLE, COMPRISING THE STEPS OF:(A) PROVIDING AN ELECTRICALLY CONDUCTIVE METALLIC SUPPORT WITH A CARBONPORTION BONDED TO SAID SUPPORT AND EXPOSED AT A SURFACE REGION THEREOF;(B) SPACEDLY JUXTAPOSING AN ELECTRODE WITH AT LEAST PART OF SAID CARBONPORTION TO FORM A SPARK GAP THEREWITH; (C) SURROUNDING THE JUXTAPOSEDPARTS OF SAID ELECTRODE AND SAID CARBON PORTION WITH AN AMBIENT LIQUIDFILLING SAID GAP; AND (D) EFFECTING AT LEAST ONE IMPULSIVE SPARKDISCHARGE ACROSS SAID GAP BETWEEN SAID CARBON PORTION AND SAID ELECTRODEWITH SUFFICIENT DISCHARGE ENERGY TO GENERATE A TEMPERATURE AND PRESSURECONVERTING AT LEAST PART OF SAID CARBON PORTION TO DIAMOND.